My Dual Battery Setup- Diagram Check

[ntsqd]

This would be an ideal place for Firebraid sleeving. Woven fibreglas tube covered in high temp orange silicone.

Longacre p/n 49750 36" for $21.50 or p/n 49770 10' for $57.35
Use adhesive lined heat shrink on each end of the sleeve to keep grit from getting in and slowly grinding thru the cable's insulation.

 

[Dusty T.]

That looks to be pefect for that application, thanks!

What I'll probably do is cover the charge wires in split wire loom (swear by that stuff for finish and longevity), and then run the Firebraid sleeving over the loom..... I called Longacre to double-check and according to them that is acceptable.

Thanks.

 

[Dusty T.]

Well, I've kicked off the ordering process, and purchased the BIC 95150B yesterday. Mike has patiently answered numerous questions I've emailed to him, and I think this product will work nicely for my setup.

I did come up with one snafu now that I am getting ready to order up wire. The length between the two batteries (via the charge wire) is about 20 feet. A good long distance I know.... I used some voltage calculators to match up a good wire size and realized that the length between batteries may need to be be doubled to gain the correct voltage drop. Now, does this need to be done between two batteries, or only for branch circuits? Suddenly, the #2 charge wires (positive & negative) I was thinking about using look to be potentially too small to both charge the aux battery and run some accessories at the same time without a massive voltage drop..... I'm rethinking running the negative through the chassis since this may elliminate the return (negative) wire distance, since it is now a mass of iron....

As if this isn't overengineered enough as it is! :drool:

 

[Dusty T.]

Grounding Grounding Grounding

So, any ideas on calculating voltage drop versus using the frame as a ground, or running a dedicated wire between the two batteries?

I ask this because I went round and round about this over the past week regarding whether to use the frame as a ground or to run a dedicated negative wire back to the main battery. I also came to the realization that I could go all out and also be able to jump start the engine in an emergency situation (provided the aux battery is properly charged). This would be easily done by using the high amp marine switch to bridge the two batteries and bypass the Hellroaring isolator for higher amp current draw when starting. I have considered using the frame to ground between the two batteries, but have no idea what the resistance of the steel frame would be....

I also looked at several voltage drop calculators that seemed to indicate that the chassis or frame distance along the circuit path of travel could be disregarded when calculating voltage drop. On the other hand, when running a dedicated negative wire back to the main battery, that distance would now need to be considered. Now it seems to me that the frame would provide more resistance due to weld joints, poorer conductivity compared to copper, and the likelyhood that the current would travel through crossmembers welded to the frame rails (assuming the batteries are grounded to opposite frame rails). Not to mention resistance at the ground wire to frame connections in a wet/muddy/salty environment (and we all know how much our Tacoma frames like to corrode).

I read the arguments both for and against the dedicated ground wire. One thread I caught addressed my question nearly to a tee: http://www.exploroz.com/Forum/Topic/54859/wire__cable_size_calculations.aspx

Needless to say, I bit the bullet and purchased both positive and negative #2/0 wire to run between the main battery and bed-mounted battery (nearly a 20' distance) to be used as both the charging and starting conductors. Got a decent deal on the copper, so it didn't totally break the bank to run a dedicated ground wire back to the battery anyway.

So what's everyone's take on using the frame as a grounding conductor? I know I'm a stubborn (and possibly certifiable) fool for ordering up the extra cable at #2/0 nonetheless, I'd still like to hear other input on this grounding conundrum. My main goal after building this system is for it to be as maintenance and thought-free as possible..... :ylsmoke:

 

[keezer36]

If you've already bought enough wire, why not run it back just to be sure?
I'll be doing the voltage drop tests as discribed here: http://www.aa1car.com/library/voltage_drop_testing.htm and depending on my findings, I may do the same. I've a couple other mods on my plate right now so I don't know if I'll get to this in the next couple weeks.

 

[Dusty T.]

Hey thanks, keezer for the link. I checked it out and may give that a go after the project is built. Worst case scenario, I double up on the negative return wire by bolting it to the frame near the bed-mounted battery- thus using both the frame and wire as a ground path......

The design phase is pretty much over and parts have been trickling in this week. Installation will begin this weekend. Still getting over the price of copper these days despite working in the electrical industry! :Wow1:

 

[Dusty T.]

Well, it's finally finished after a year of starting and stopping! The battery is installed and connected, the Hellroaring isolator seems to be working as it should, with all systems up and running. There will be a writeup to follow in a couple weeks as time permits.

Got one more obscure question about cabling before I call it quits with this project. How much movement can I expect to get between the body and frame? Of course the body is mounted on rubber bushings, but how much does it really move independently of the frame itself? I ask because I'm running a battery cable that passes between the frame and cab with about 1/4" of clearance (it's been trimmed up after the pic below was taken). The same cable is also connected to the frame and then onto the body where it goes into the engine compartment. Does the cable need much if any slack for this transition? Just wondering if this is an issue when on very uneven terrain with some frame and body flex in mind.

Thanks. I'm trying to make this as robust as possible. There's a pic included showing the clearance I have.